1. Field of the Invention
The present invention relates to a non-peelable, solderable coating for metals, which is produced by electrodeposition of a water-dispersion varnish.
2. Description of the Prior Art
Organic coatings are applied to the surfaces of metals for a wide variety of reasons, such as to provide electrical insulation, to obtain corrosion resistance, to protect the metal against certain types of mechanical injury, or in the preparation of a wide variety of industrial products. In applying organic coatings, one of the more commonly used techniques is electrodeposition. Other common techniques include tumbling coating, electrostatic coating and the like.
Electrodeposition is an especially desirable technique when the coating being applied is varnish. Since the resulting coating is quite uniform without pin holes, the technique is easily automated and since no organic solvents are necessary, there is a considerable reduction in health and safety hazards as compared with the techniques for coating varnish.
In the electrodeposition of a varnish, a water soluble type paint is first prepared using a resin which has good membrane forming qualities. The molecular weight of the resin is usually in the several thousand range, and often, the resin will have some dissociating group. Such water soluble resin type varnishes provide very high covering performance, even for metallic articles of intricate shapes.
Heretofore however, the thickness of the coating has been somewhat limited, and has generally been restricted to coatings of only a few more microns.
If electrodeposition is to be successfully carried out, it is essential that the polymer used in forming the varnish have dissociated groups in the polymer chain, otherwise the varnish cannot act as an electrolyte and hence the electrode-position will not proceed. Because of the dissociated groups however, the water soluble varnishes provide generally non-uniform electrical characteristics, and hence they are unsuitable for use as electrical insulation.
The applicants have now developed a new resin for use in forming an electrodeposition varnish, which has a relatively small number of dissociated groups, as compared with prior art resins. The resin of this invention can be used to prepare coated membranes which are characterized by excellent mechanical properties, good chemical resistance, good water resistance, and good electrical characteristics, such as volume resistivity and breakdown voltage. The resin of this invention can further provide a quite thick coating, although it does suffer the disadvantage that the coatings produced on intricate shaped substrates are often somewhat non-uniform.
Heretofore, polyurethane has been used to coat wires used for home electrical equipment and communication equipment, such as television and radio circuits. The main reason for the use of polyurethane coated wire is that it is highly solderable and will not peel readily from the wire. Moreover, it possesses good solderability which is important for these applications.
A need exists therefore for a varnish which can be used to provide relatively thick coatings, which is highly solderable and will not peel readily from the substrate surfaces, and which does not provide the disadvantages normally resulting from the use of a resin varnish wherein the resin has a large number of dissociated groups.